1. Field of the Invention
The present invention relates to an optical frequency multiple signal processing method of processing at high speed an optical frequency multiple signal multiplexed in frequency domain.
2. Description of Related Art
FIG. 1 is a schematic view showing a construction of a conventional optical frequency multiple signal recording apparatus shown, for example, in U.S. Pat. No. 4,101,976 (1978). In the figure, reference numeral 10 designates a laser generating a laser beam of variable wavelength and the frequency of laser beam generated from the laser 10 is varied by a scanner 11. A filter 12 making only laser beam of selected frequency to pass therethrough, a filter 13 modulating irradiating condition of the outgoing light from the laser 10, an optical recording medium 14 recording a signal, and a photo detector 15 detecting a light having passed through the optical recording medium 14 are optically connected with the laser 10 in this order. The filter 13 modulates the irradiation intensity and irradiation time of the outgoing light from the laser 10 so that a new signal may not be recorded in the optical recording medium 14 in regenerating a signal from the optical recording medium 14.
Next, explanation will be given on the operation. FIG. 2(a) shows a light absorption spectrum of the optical recording medium 14 before the recording of signal. The optical recording medium 14 has optical saturation characteristic and has an inhomogeneous broadening of absorption line in optical frequency band .omega.A-.omega.B, and when it receives light, there is generated a photo-induced reaction. The photo-induced reaction is a photochromic reaction or a photo-chemical reaction.
When light of intense spectral distribution as shown in FIG. 2(b) is irradiated to the optical recording medium 14, dips are generated in the light absorption spectrum as shown in FIG. 2(c), and there is generated a spectral hole (hereinafter to be called a hole). This phenomena is known as photochemical hole burning, and signals are multiplexed and recorded in frequency domain according to the presence of the hole.
Signals are recorded by the fact that the light generated at the laser 10 is frequency-selected by the scanner 11 and the filter 12, thereby to generate holes successively in the optical recording medium 14. And in regenerating recorded signal, the light generated at the laser 10 is frequency-scanned over a band of .omega.A-.omega.B. At this time, the irradiation time and irradiation intensity of the light generated at the laser 10 is modulated by the filter 13 in order to prevent a hole burning from generating in recording signal. Owing to the frequency scanning, the output of the photo detector 15 shows its peak when the frequency of the light generated at the laser 10 coincides with the frequency corresponding to the respective holes, thereby regenerating signal can be obtained in time sequence.
As the conventional optical frequency multiple signal recording apparatus is so constructed as abovementioned, there is a problem that an optical signal processing apparatus conventionally used does not cope with optical frequency multiple signal recording using multiple signal of such a specific frequency domain.
In addition, in regenerating signal recorded in the optical recording medium, as light for regenerating signal must be frequency-scanned, there are problems that a device performing the frequency-scanning of light is needed and also a long time is required for the frequency-scanning of light.